nir: Allow nir_var_mem_global variables

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15486>

src/compiler/nir/nir.c

@@ -286,11 +286,8 @@ nir_shader_add_variable(nir_shader *shader, nir_variable *var)
    case nir_var_shader_call_data:
    case nir_var_ray_hit_attrib:
    case nir_var_mem_task_payload:
-      break;
-
    case nir_var_mem_global:
-      assert(!"nir_shader_add_variable cannot be used for global memory");
-      return;
+      break;
 
    default:
       assert(!"invalid mode");

src/compiler/nir/nir.h

@@ -3614,6 +3614,9 @@ typedef struct nir_shader {
     */
    unsigned num_inputs, num_uniforms, num_outputs;
 
+   /** Size in bytes of required implicitly bound global memory */
+   unsigned global_mem_size;
+
    /** Size in bytes of required scratch space */
    unsigned scratch_size;
 

src/compiler/nir/nir_intrinsics.py

@@ -806,6 +806,7 @@ system_value("aa_line_width", 1)
 system_value("scratch_base_ptr", 0, bit_sizes=[32,64], indices=[BASE])
 system_value("constant_base_ptr", 0, bit_sizes=[32,64])
 system_value("shared_base_ptr", 0, bit_sizes=[32,64])
+system_value("global_base_ptr", 0, bit_sizes=[32,64])
 
 # System values for ray tracing.
 system_value("ray_launch_id", 3)

src/compiler/nir/nir_lower_io.c

@@ -886,6 +886,7 @@ build_addr_for_var(nir_builder *b, nir_variable *var,
 {
    assert(var->data.mode & (nir_var_uniform | nir_var_mem_shared |
                             nir_var_mem_task_payload |
+                            nir_var_mem_global |
                             nir_var_shader_temp | nir_var_function_temp |
                             nir_var_mem_push_const | nir_var_mem_constant));
 
@@ -913,6 +914,10 @@ build_addr_for_var(nir_builder *b, nir_variable *var,
          base_addr = nir_load_shared_base_ptr(b, num_comps, bit_size);
          break;
 
+      case nir_var_mem_global:
+         base_addr = nir_load_global_base_ptr(b, num_comps, bit_size);
+         break;
+
       default:
          unreachable("Unsupported variable mode");
       }
@@ -940,6 +945,10 @@ build_addr_for_var(nir_builder *b, nir_variable *var,
          assert(var->data.driver_location <= UINT32_MAX);
          return nir_imm_intN_t(b, var->data.driver_location | 1ull << 62, 64);
 
+      case nir_var_mem_global:
+         return nir_iadd_imm(b, nir_load_global_base_ptr(b, num_comps, bit_size),
+                                var->data.driver_location);
+
       default:
          unreachable("Unsupported variable mode");
       }
@@ -2327,6 +2336,9 @@ lower_vars_to_explicit(nir_shader *shader,
    case nir_var_mem_task_payload:
       offset = shader->info.task_payload_size;
       break;
+   case nir_var_mem_global:
+      offset = shader->global_mem_size;
+      break;
    case nir_var_mem_constant:
       offset = shader->constant_data_size;
       break;
@@ -2373,6 +2385,9 @@ lower_vars_to_explicit(nir_shader *shader,
    case nir_var_mem_task_payload:
       shader->info.task_payload_size = offset;
       break;
+   case nir_var_mem_global:
+      shader->global_mem_size = offset;
+      break;
    case nir_var_mem_constant:
       shader->constant_data_size = offset;
       break;
@@ -2411,6 +2426,8 @@ nir_lower_vars_to_explicit_types(nir_shader *shader,
 
    if (modes & nir_var_uniform)
       progress |= lower_vars_to_explicit(shader, &shader->variables, nir_var_uniform, type_info);
+   if (modes & nir_var_mem_global)
+      progress |= lower_vars_to_explicit(shader, &shader->variables, nir_var_mem_global, type_info);
 
    if (modes & nir_var_mem_shared) {
       assert(!shader->info.shared_memory_explicit_layout);

src/compiler/nir/nir_validate.c

@@ -1772,6 +1772,7 @@ nir_validate_shader(nir_shader *shader, const char *when)
       nir_var_system_value |
       nir_var_mem_ssbo |
       nir_var_mem_shared |
+      nir_var_mem_global |
       nir_var_mem_push_const |
       nir_var_mem_constant |
       nir_var_image;